1. Field of The Invention
The present invention relates to an apparatus for controlling each damping coefficient of four shock absorbers, each shock absorber being interposed between a vehicle body and its respective road wheel, so as to provide an optimum damping force (the shock absorber is also termed damper but hereinafter referred to as shock absorber).
2. Description of The Background Art
A Japanese Patent Application First Publication No. Showa 61-163011 published on Jul. 23, 1986 exemplifies a previously proposed damping coefficient controlling apparatus which detects an sprung mass speed and a relative speed between sprung mass and an unsprung mass speeds. When both of the respective speed values have mutually the same sign (+ or -), the damping coefficients of the respective shock absorbers are in hard positions (in high damping coefficients). When both of them have the mutually different signs (+ or -), the damping coefficients are set to positions of soft damping coefficients. Such a control operation as described above is carried out independently for each shock absorber.
However, in the previously proposed damping coefficient controlling apparatus, in a case where the damping coefficients are optimally set to the hard damping coefficients when the vehicle body is in a bouncing motion, a vehicular body inertia moment with a vehicular weight center as a center is added to the sprung mass in a case where such a bouncing motion as described above is associated with, e.g., a pitching motion of the vehicle body. At this time, the damping force generated in the case where the high damping coefficients are set is insufficient and the steering stability of the vehicle is deteriorated.
In addition, another damping coefficient controlling apparatus has been proposed in which a rolling and/or pitching suppression control toward the suspension system is carried out independently for each other of the shock absorbers.
However, in the latter previously proposed damping coefficient controlling apparatus, another extra sensor such as a steering angle sensor is required and each shock absorber is still independently controlled.